The pleas from the border came as authorities in Texas reported other evidence of Mexican drug violence in the US, including a bullet-riddled truck found on the US side of the border last week with the bodies of two Mexican nationals inside – an act of violence that Brownsville Police Chief Carlos Garcia described as a cartel-ordered "hit."

"The larger significance of [the pirate attack] is whether it's an indicator of what we greatly fear, which is that violence would spill over [the US border] in a direct way," says Robert Chesney, a national security law expert at the University of Texas, in Austin.

President Obama sent 1,200 National Guard troops to the border earlier this year, and locals on Falcon Lake report a step-up in patrols of the US side of the 60-mile-long basin, which is part of the Rio Grande watershed and managed by a binational commission.

In the wake of the alleged attack on Falcon Lake, the US government has renewed warnings to boaters not to cross the midlake border, which is marked by concrete columns, to minimize risks of running into pirates.

Authorities report five incidents this year in which bass fishermen were either robbed at gunpoint or approached by pirates before escaping, including the most recent report where a boat marked with a misspelled "Game Wardin" tried to get close to fishermen, who grew suspicious and fled.

Attacks on Falcon Lake are likely a direct outcome of pressure on the cartels, both from law enforcement and competing drug gangs, that has pushed smugglers to diversify to supplement their incomes. The Zetas used to be the enforcers for the Gulf Coast Cartel before essentially staging a coup and taking over much of the cartel's drug-running.

Drug and human traffickers "are increasingly confrontational … which is illustrated by spillover violence," Governor Perry said in a statement on Monday. Perry urged the Obama administration to deploy weaponized drone airplanes to patrol the lake and the border.

With tears running down her face, Ms. Hartley described her Sept. 30 ordeal on NBC's "Today Show" on Tuesday. She said three boats approached her and her husband on the Mexican side of the lake, after the couple had visited the famous half-submerged church ruins at Old Guerrero.

The men in the boats, she said, opened fire on the couple and Mr. Hartley was struck in the back of the head. As bullets whizzed into the water, she said, she tried unsuccessfully to return to pick him up, but was forced to hightail it toward US waters. Eyewitnesses say the presumed pirates chased Hartley into the US section of the lake.

Mexican authorities on Tuesday raised questions about the veracity of Hartley's story. "We are not sure. We are not certain that the incident happened the way they are telling us," Marco Antonio Guerrero Carrizales, district attorney for the Miguel Aleman Province, said in a statement, according to CBS News.

The Mexican district attorney questioned why neither Hartley's body nor his Jet ski have been found. Hartley and some US authorities suggest the pirates may have carried off Hartley and his craft to hide the evidence.

"As far as we know, we don't think they have been looking. And there is – we understand the possibility that the people who did this probably have him. And that's why maybe they can't find him," Ms. Hartley said on the "Today Show."

The issue of spillover violence is a key link in the political debate over immigration reform in the US. Arizona officials have used the example of a slain rancher, kidnappings in Phoenix, and unconfirmed reports of headless bodies found in the desert to justify law enforcement crackdowns.

The US Department of Justice won a partial judgment against Arizona this summer, gutting a controversial new law that would have required residents to carry their immigration papers at all times in case a law enforcement officer wanted to take a look.

Drug violence in Mexico has claimed some 26,000 lives since 2006, mostly cartel members and police.

According to Professor Chesney, cartels have been careful not to involve the US in the drug war so as avoid drawing retaliation from their wary neighbor. Even though the Falcon Lake incident may not be evidence that Mexico's drug violence is seeping over the border in new ways, such incidents could ratchet up pressure on the Obama administration to act, he says.